1 (a) Field of the Invention
This disclosure relates to a method of preparing a graphene nanoplate, a graphene nanoplate prepared according to the method, and a graphene nanoplate paste and a conductive layer including the same.
1 (b) Description of the Related Art
Graphene prepared from graphite may be classified into two types according to a thickness of the graphite. In other words, a reduce grapheme oxide (RGO) that has the number of a graphene layer of less than about 10 and a graphene nanoplate (GNP) that has a thickness of several nm to about 100 nm. The RGO may be prepared by chemical or thermal reduction of graphene oxide (or graphite oxide, GO) that is produced by oxidation treatment of graphite, and the graphene nanoplate may be prepared by exfoliating graphite physicochemically. Specifically, a graphene nanoplate is prepared using an intercalated carbon compound (ICC) including chemical species among graphite layers, and herein, when the ICC is microwave-treated or heat-treated, the chemical species inserted among the graphite layers is output as gas phases and expands a space among the graphite layers to produce an expanded graphite (EG), and the graphene nanoplate may be prepared by breaking (cracking process between partially connected inter-GNP layers) the expanded graphite.
A conventional method for preparing a graphene nanoplate may be classified into a liquid ultrasonication cracking method, a cracking method using a rheological shear stress, a solid-phase-solid-phase or liquid mechanical cracking method (e.g., ball milling, grinding, and the like), and the like based on a method of breaking the expanded graphite. In addition, the graphene nanoplate may be prepared using the same method but have various properties based on a process condition, that is, a microwave treatment condition (e.g., intensity/atmosphere/treatment time/treatment environment, and the like), a heat treatment condition (e.g., temperature/atmosphere: vacuum furnace, heating speed, treatment time/treatment method and the like), and the like.
In the liquid-phase ultrasonication cracking method, a graphene nanoplate is prepared when expanded graphite is broken by a strong impact produced when micro-cavity produced by ultrasonication is repetitively contracted and expanded and then, exploded. This method has an advantage of preparing a graphene nanoplate in a lab environment and preparing substantially low concentration graphene nanoplate dispersion by adding a dispersing agent. However, the method is performed in a liquid and has a limit in a solvent and thus, is adjusted based on a grinding and dispersion condition in a desired solvent, and in addition, and the solvent needs to be evaporated again to obtain a powder from a solution.
The cracking method using a rheological shear stress is a method of forcing liquid-supported expanded graphite into a minute space using a high pressure (e.g., thousands of bars) to grind the expanded graphite and has similar merits and drawbacks to the liquid-phase ultrasonication cracking method. The solid-phase-solid-phase or liquid-phase mechanical cracking method is performed by mixing minute balls with the expanded graphite (herein, a solvent may be partly added thereto) and milling the expanded graphite, and herein, the expanded graphite is ground by energy generated on the interface when the balls collide. However, the produced graphene nanoplates contact one another and are stuck together. Accordingly, in the present invention, a pure graphene nanoplate may be prepared using an ICC raw material to prepare expanded graphite but a novel method of complementing the problems of the conventional methods.
In addition, in the present invention, industrial application (e.g., composite paste) of the graphene nanoplate by combining the graphene nanoplate with a heterogeneous material may be enlarged. Combinations between heterogeneous materials are important, and this may improve properties by synergic effects between materials exceeding a limit of the conventional material. The heterogeneous mixture may be used in a high strength composite material and a fuel cell. As a representative technologies, a graphene-nanowire (e.g., semiconductor) hybrid structure where light energy is absorbed in a graphene conductive part and electron-hole pairs may be generated, a method of preparing a hybrid composite including graphene sheet/carbon nanotube/a polymer nano particle, a method of preparing a positive electrode material for a lithium rechargeable battery graphene that is a hybrid material by adding a Fe precursor and a phosphate (PO4) precursor, a method of preparing a graphene composite calcinated body having improved charge and discharge ratio by sintering graphene and a metal oxide particle in an air, a method of preparing a graphene-titanium dioxide (TiO2) hybrid material by mixing a nano TiO2 powder with graphene at a high temperature and high pressure and reacting them, and the like. The present invention relates to a method of preparing good quality of a graphene nanoplate by a novel method and its application (e.g., paste and conductive layer).